Manufacture of insulated electric conductors



Aug. 9, 1960 H. R. LORCHY ETAL 2,948,647

MANUFACTURE OF INSULATED ELECTRIC CONDUCTORS Filed March 7, 1955 3 Sheets-Sheet 1 Inventors l/ewbarm Ric/11rd Lord 21 Jame: Aitptander t/80C By v M/ y Q H. R. LORCH ETAL Aug. 9, 1960 I I I MANUFACTURE OF INSULATED ELECTRIC CONDUCTORS Filed March 7, 1955 3 Sheets-Sheet 2 Inventors l/ermzm Rich/rd torch z! dame; Alexander MC'leeqy v By W P A ttorney:

Aug. 9, 1960 H. R. LORCH ET AL 2,943,647

MANUFACTURE OF INSULATED ELECTRIC CONDUCTORS Filed March 7, 1955 5 Sheets-Sheet a mmik lnvenlors l/ermannfikbarc/ lore/1 V Jame; Akxandpr-M'C'Iefly B M 7%) Attorney;

United States Patent Ofiice MANUFACTURE OF INSULATED ELECTRIC CONDUCTORS Hermann Richard Lorch, Southport, and James Alexander McCleery, Sale, England, assignors to British Insulated Callenders Cables Limited, London, England, a British company Filed Mar. 7, 1955, Se!- N 492,545 Claims priority, application Great Britain Mar. 12, 1954 7 Claims. c1. 1542.28)

This invention relates to the manufacture of insulated electric conductors of the kind comprising one or more wires embedded in a body of compressed heat-resistant powder serving as the insulant, the whole being enclosed in a tube of metal. The method of manufacture is of the kind comprising the following steps: extruding on the conductor, or conductors, a covering of paste contain-- ing the powdered insulant and water, drying the paste, applying a sheath over the covering and finally drawing down the sheath to consolidate and compress the powder. In such a method it has already been proposed to dry the paste before the sheath is applied.

The present development is based on the discovery that by establishing suitable conditions it is practicable to sheath the cable while the paste is still wet and dry the insulant after sheathing has been completed.- The rocedure in accordance with the invention comprises extruding the paste on the wire or wires; applying to the outside of the paste a pervious C6VIifig extruding the sheath over the covered paste with asmall clearance, as hereinafter defined; putting the coil of sheathed conductor in an oven', where itis heated for a time and at a temperature appropriate for securing drying; and then drawing down the sheath to remove the clearance and consolidate" and 'c'ompress the powder. The coil may or -rnay not becomes before drawing down the sheath. The assembly may also be further drawndown for elong'ation of sheathand conduct'ors if required.

The pervious covering is preferably a layer" of thin metal foil inthe form of a tape applied about the paste either as a helical lapping or by longitudinally folding it into a tube. adjacent edges of the tape will not be sealed. When in the ofhelical lappingthere is preferably a small degree of overlapping between adjacent turns. The tape covering ensures the holding of the paste in positioii while permitting the escape of steam between theadjacent edges.

Soir'i'e drying of the paste may occur between the application of this covering and the application of the sheath, since the covered body will usually remain in the atmosphere of the factory for some appreciable time between these steps, and a considerable part of the moisture may be evaporated this way. The final and more important stage of the drying will, however, be carried out in the oven.- The coiling of the core at the intermediate stage is preferably done in a single layer on a drum.

The selection of the appropriate clearance between core and sheath is of importance, If it is too small the steam will not be able to travel freely along it and a blockage will take place with a possibility of bursting of the sheath. If the clearance is excessive uneven elongation of the sheath and conductor may occur during the initial stages of the drawirig d'own, resulting in the production' er fissures and gaps in the body of irisulaiit. The small clearance above referred to is that which avoids these two extremes. An example of a suitable value for In either event the joint between the 2,948,647 Patented Aug. 9, 19b0 a core diameter of inch is that obtained by making Figure 1 represents in part section the applicatioii of the insulant and pervious covering in the manufacture of a twin conductor cable;

Figure 2, also in part section, illustrates the extrusion of the sheath on the core made as shown in Figure 1,

Figure 3 represents in part section the arrangement of a number of coils of sheathed cable in a drying chamber;

Figure 4' illustrates in part section the process of draw= ing down the sheath; v

Figure 5 is a plan illustrating an alternative manner of applying a pervious covering to the insulated wires;

Figure 6 is a side view of the arrangement shown in Figure 5; and p Figure 7 is a cross=s ectional View, not to a scale, of the cable before the sheath is drawn down on to the core.

Figure 8 is an enlarged segmental view of the extra sion nozzle of Figure 2. p I

Referring first to Figure 7, the cable comprises two single conductor Wires 1, 2 embedded in, so as to be completely surrounded and insulated from one another by, an extruded body of insulating composition 3. This composition when dry comprises compressed powdered talc and bentom't'e. Over the insulation 3 there is a pervions covering 4 comprising a helical wrapping of aluminum tape applied with overlapping turns. Overall is an extruded aluminum sheath 5. This represents the cable prior to being subject to drawing down iii the manner hereinafter described with reference to Figure 4, and in this stage there exists between the sheath 5' and the pervious' covering 4 a small clearance 6 which permits the escape of steam along the length of the cable duringthe drying of the insulation 3.

In the first stage of manufacture the conductors 1 2 are drawnfrorn two reels 7', 8 through a paste extruding machine 9; The paste 3 is forced by the usual means" 14 is rotatably mounted a holder 15 for a pad 1 6 or aluminum tape in the form of a flat spiral. From pad 16 the tape 4 is led over a guide 18 to core body 1-2.

-The holder 15 is rotated by an appropriate drive 17,

thus rotating the guide 18 about the advancing core body 12 and applying the tape 4 helically with overlaI Piii turns as illustrated in Figure 4. The taped core 19 thus formed is taken up in a single layer on a drum 20. v This drum 20 is conveniently rotated by driving rolls 2.1 on

which it rests and at the same time is caused to move sideways in order to control the even distribution of the single layer winding. The device for producing the side ways movement is diagrammatically represente'dby the threaded shaft 22 controlled by a gear box 23'. drum 20 is now mounted at the back 'of a metal extrusion machine 24, as shown in Figure 2 for the application' of the aluminum sheath 5 with a small clearance The extrusion machine comprises inthe usual manner two'plungers 25 which press the metal 26 out of two con Other pastes may be used; for instance one tainers into an extrusion chamber 27 where the sheath is formed between two die elements 23 and 29. The sheath is applied with the small clearance 6 shown diagrammatically in Figures 4 and 7. The sheathed cable is taken up in the form of a coil 30 on a swift 31 rotated in any convenient manner about a vertical spindle 32.

The coil is now transferred to a drying oven 33 shown diagrammatically in section in Figure 3. In the illustration there are shown a number of coils 30 stacked one on top of another in the oven. The coils 30 are completely enclosed in the oven with the ends 34 of the sheaths open to permit the escape of steam. Heating elements 35 are arranged in the wall of the oven and there is provided an entry 36 for dry air and an exit 37 for the steam escaping from the ends of the cable.

After drying the sheathed cable is drawn through a die 38 illustrated in Figure 4. The die has a conical working face 39 and in being drawn through it the diameter of the sheath is reduced to eliminate all the clearance space 6, thus leaving the sheath tight on the metal taped insulation. The cable may be drawn through subsequent dies to finally compress and consolidate the insulation and may be afterwards drawn down again to obtain elongation of the complete cable.

In Figures 5 and 6 there is shown the formation of the pervious covering from an aluminum tape 40 folded longitudinally about the core body 12 as it leaves the paste extruder 9, the latter not being shown in these figures. The tape 40 is drawn from a coil 41 mounted beneath the advanced core body 12 and rotatable about an axis 42 extending at right angles to the direction of movement of the core body. The core body and tape are drawn together through a tapered die 43 which forms the tape into a cylindrical cover about the underlying insulation. At the seam 44 the edges of the tape may butt against one another or may not completely meet or may slightly overlap. There being no seal between the edges of the tape, the moisture is permitted to escape from the insulation during the drying process. The other stages in the manufacture of this cable are identical with these already described in connection with the other figures.

For the heating it is important that the coil should be completely enclosed in the oven and the heating carried out so as to obtain substantial uniformity of rise of temperature throughout the length of the coil, thus avoiding the possibility of local condensation of steam. The time and temperature of heating are so adjusted as to obtain complete drying in a reasonable time. On the other hand the rise in temperature should be so regulated that the rate of evolution of steam does not become excessive at any stage. An example of a suitable procedure is raising the temperature gradually to about 400 C. and holding it there from two to four hours. Since at this temperature the coil is too hot for convenient handling and may also damage the usual lubricant used in the subsequent drawing down operation, it will usually be allowed to cool but not necessarily to room temperature.

The improved procedure has important advantages in facilitating the organisation of the manufacture, since the several definite steps in the manufacture can take place without any close correlation in time.

What we claim as our invention is:

1. A method of making an electric cable comprising in sequence the steps of extruding about a wire a body of paste containing powdered heat-resisting insulant and. water, enclosing the body of paste in a pervious covering, extruding over the covered paste body a metal sheath with a small clearance between the sheath and the body, said small clearance having a transverse dimension less: than the transverse dimension of the body and being sufficient to provide a free path for the travel of steam along the cable, coiling the metal sheathed body and heating the coiled body in an oven to dry the insulant and finally drawing down the metal sheath to remove the clearance.

2.. A method of making an electric cable comprising in sequence the steps of extruding about a wire a body of paste containing powdered heat-resisting insulant and water, wrapping the body of paste with thin tape, the edges of the tape providing between them a passage for the escape of steam from the paste body, extruding over the tape-covered body a metal sheath with a small clearance between the sheath and the body, said small clearance having a transverse dimension less than the transverse dimension of the body and being suflicient to provide a free path for the travel of steam along the cable, coiling the metal sheathed body and heating the coiled body in an oven to dry the insulant and drawing down the metal sheath to remove the clearance.

3.- A method of making an electric cable comprising in sequence the steps of extruding about a wire a body of paste containing powdered heat-resisting insulant and water, covering the paste body with a helical wrapping of thin metal tape with overlapping turns providing between them a passage for the escape of steam from the paste, extruding over the tape-covered body a metal sheath with a small clearance between the sheath and the body, said small clearance having a transverse dimension less than the transverse dimension of the body and being suflicient to provide a free path for the travel of steam along the cable, coiling the metal sheathed body and heating the coiled body in an oven to dry the insulant and finally drawing down the metal sheath to remove the clearance.

4. A method of making an electric cable including in sequence the steps of extruding about a wire a body of paste containing powdered heat-resisting insulant and water, covering the paste body with a metal tape extending parallel with the body and bent transversely into a tube enclosing the body with the adjacent edges of the tape providing between them a passage for the escape of steam from the paste, extruding over the tape-covered body a. metal sheath with a small clearance between the sheath and the body, said small clearance having a transverse dimension less than the transverse dimension of the body and being sufficient to provide a free path for the travel of steam along the cable, coiling the metal sheathed body and heating the coiled body in an oven to dry the insulant and drawing down the metal sheath to remove the clearance.

5. A method of making an electric cable comprising in sequence the steps of completely embedding at least two wires in an extruded body of paste containing powdered heat-resistant insulant and water, enclosing the body of paste in a pervious covering, extruding over the covered paste body a metal sheath with a small clearance between the sheath and the body, said small clearance having a transverse dimension less than the transverse dimension of the body and being sufiicient to provide a free path for the travel of steam along the cable, coiling the metal sheathed body in an oven to dry the insulant and finally drawing down the metal sheath to remove the clearance.

. 6. A method of making an electric cable including in sequence the steps of extruding about a wire a body of paste containing powdered heat-resistant insulant and water, enclosing the body of paste in a pervious covering, extruding over the covered paste body a metal sheath with a small clearance between the sheath and body, said small clearance having a transverse dimension less than the transverse dimension of the body and being sufficient to provide a free path for the travel of steam along the cable, coiling the metal sheathed body, raising the temperature of the coiled body uniformly throughout its length to the drying temperature of the paste, maintaining the drying temperature for a period to dry the paste and finally drawing down the metal sheath to re move the clearance.

7, A method. of making an electric cable including in sequence the steps of extruding about a wire a body of paste containing powdered heat-resistant insulant and water, enclosing the body of paste in a pervious covering, extruding over the covered paste body a metal sheath with a small clearance between the sheath and body, said small clearance having a transverse dimension less than the transverse dimension of the body and being sufiicient to provide a free path for the travel of steam along the cable, coiling the metal sheathed body, raising the temperature of the coiled body uniformly throughout its length to the drying temperature of the paste, maintaining the drying temperature for a period to dry the paste, cooling the coiled body and finally drawing down the metal sheath to remove the clearance.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS Great Britain Dec. 14, 1936 Great Britain Oct. 27, 1949 Switzerland Jan. 15, 1948 Australia Dec. 4, 1952 

1. A METHOD OF MAKING AN ELECTRIC CABLE COMPRISING IN SEQUENCE THE STEPS OF EXTRUDING ABOUT A WIRE A BODY OF PASTE CONTAINING POWERED HEAT-EXTRUDING ABOUT A WIRE A BODY WATER, ENCLOSING THE BODY OF PASTE IN A PERVIOUS COVERING, EXTRUDING OVER THE COVERED PASTE BODY A METAL SHEATH WITH A SMALL CLEARANCE BETWEEN THE SHEATH AND THE BODY, SAID SMALL CLEARANCE HAVING A TRANSVERSE DIMENSION LESS THAN THE TRANSVERSE DIMENSION OF THE BODY AND BEING SUFFICIENT TO PROVIDE A FREE PATH FOR THE TRAVEL OF STEAM ALONG THE CABLE, COILING THE METAL SHEATHED BODY AND HEATING THE COILED BODY IN AN OVEN TO DRY THE INSULANT AND FINALLY DRAWING DOWN THE METAL SHEATH TO REMOVE THE CLEARANCE. 